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Aviation safety reports, made easier to study

NTSB Reports is an independent research and search tool for public aviation accident and incident records. It brings NTSB aviation reports, structured fields, docket files, extracted figures, photos, videos, and update history into one searchable interface.

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April 21, 1990 · Bell 206B3 · N1075G

Williamsport, AK

Overview

Report Status
Probable Cause
Event Type
Accident
Date
April 21, 1990
Injury Outcomes
No injuries (4 uninjured)
Location
Williamsport, AK
Aircraft
Bell 206B3
Tail Number
N1075G
Injuries
None
Aircraft Damage
Substantial
NTSB Number
ANC90LA063

THE HELICOPTER PILOT REPORTED A TOTAL LOSS OF POWER AND A SUBSEQUENT HARD AUTOROTATION LANDING. AN EXAMINATION OF THE ENGINE DISCLOSED A FRACTURED PC TUBE FROM THE COMPRESSOR TO THE PC FILTER. FAILURE OF THIS TUBE WILL CAUSE THE ENGINE TO LOSE POWER BELOW IDLE OR FLAME OUT. AN NTSB METALLURGIST WHO EXAMINED THE TUBE BELIEVES THAT THE TUBE FRACTURED DUE TO FRETTING AND FATIGUE, MOST LIKELY PRECIPITATED BY MISALIGNMENT OF THE PC TUBE DURING FIELD MAINTENANCE. ALLISON, THE ENGINE MANUFACTURER, HAS RECENTLY REDESIGNED THE TUBE WITH A THICKER WALL AND A DIFFERENT SHAPE TO FACILITATE MAINTENANCE PROCEDURES IN THE FIELD, AND TO MAKE THE TUBE MORE RESISTANT TO FATIGUE.

NTSB Probable Cause

THE MANUFACTURER'S INADEQUATE PART DESIGN AND THE IMPROPER MAINTENANCE TECHNIQUES BY THE OPERATOR.

Full Narrative

THE HELICOPTER PILOT REPORTED A TOTAL LOSS OF POWER AND A SUBSEQUENT HARD AUTOROTATION LANDING. AN EXAMINATION OF THE ENGINE DISCLOSED A FRACTURED PC TUBE FROM THE COMPRESSOR TO THE PC FILTER. FAILURE OF THIS TUBE WILL CAUSE THE ENGINE TO LOSE POWER BELOW IDLE OR FLAME OUT. AN NTSB METALLURGIST WHO EXAMINED THE TUBE BELIEVES THAT THE TUBE FRACTURED DUE TO FRETTING AND FATIGUE, MOST LIKELY PRECIPITATED BY MISALIGNMENT OF THE PC TUBE DURING FIELD MAINTENANCE. ALLISON, THE ENGINE MANUFACTURER, HAS RECENTLY REDESIGNED THE TUBE WITH A THICKER WALL AND A DIFFERENT SHAPE TO FACILITATE MAINTENANCE PROCEDURES IN THE FIELD, AND TO MAKE THE TUBE MORE RESISTANT TO FATIGUE.

Flight

Event TypeAccident
Event Time13:10 AKDT
Nearest AirportIliamna Bay (0nm N)
Runway0
Flight Plan FiledVFR
Aircraft FireNo
Aircraft ExplosionNo

Aircraft

AircraftBell 206B3
Tail NumberN1075G
Aircraft CategoryHeli
DamageSubstantial
Operating RulePart 135
Engines1
Engine TypeTurboshaft
Engine DetailsAllison · 250-C20B · Turboshaft · 420
Seats5

People & Injuries

Injury SummaryNo injuries (4 uninjured)
Fatal0
Serious0
Minor0
Uninjured4
Total4
Crew 1Age 43 · First Class

Conditions

ConditionsVMC
LightDaylight
Wind115° @ 10 kt, gusting 5 kt
Visibility100 sm
CeilingNone
Temperature / Dew Point39 C / 0 C
Altimeter0
Weather SourcePILO

External Links

Appendix: Source Data